As an important component of ecosystem carbon(C) budgets, soil carbon dioxide(CO_2) flux is determined by a combination of a series of biotic and abiotic processes. Although there is evidence showing that the abiotic component can be important in total soil CO_2 flux(R_(total)), its relative importance has never been systematically assessed. In this study, after comparative measurements of CO_2 fluxes on sterilized and natural soils, the R_(total) was partitioned into biotic flux(R_(biotic)) and abiotic flux(R_(abiotic)) across a broad range of land-cover types(including eight sampling sites: cotton field, hops field, halophyte garden, alkaline land, reservoir edge, native saline desert, dune crest and interdune lowland) in Gurbantunggut Desert, Xinjiang, China. The relative contribution of R_(abiotic) to R_(total), as well as the temperature dependency and predominant factors for R_(total), R_(biotic) and R_(abiotic), were analyzed. Results showed that R_(abiotic) always contributed to R_(total) for all of the eight sampling sites, but the degree or magnitude of contribution varied greatly. Specifically, the ratio of R_(abiotic) to R_(total) was very low in cotton field and hops field and very high in alkaline land and dune crest. Statistically, the ratio of R_(abiotic) to R_(total) logarithmically increased with decreasing R_(biotic), suggesting that R_(abiotic) strongly affected R_(total) when R_(biotic) was low. This pattern confirms that soil CO_2 flux is predominated by biotic processes in most soils, but abiotic processes can also be dominant when biotic processes are weak. On a diurnal basis, R_(abiotic) cannot result in net gain or net loss of CO_2, but its effect on transient CO_2 flux was significant. Temperature dependency of R_(total) varied among the eight sampling sites and was determined by the predominant processes(abiotic or biotic) of CO_2 flux. Specifically, R_(biotic) was driven by soil temperature while R_(abiotic) was regulated by the change in soil temperature(ΔT). Namely, declining temperature(ΔT<0) resulted in negative R_(abiotic)(i.e., CO_2 went into soil) while rising temperature(ΔT>0) resulted in positive R_(abiotic)(i.e., CO_2 released from soil). Without recognition of R_(abiotic), R_(biotic) would be overestimated for the daytime and underestimated for the nighttime. Although R_(abiotic) may not change the sum or the net value of daily soil CO_2 exchange and may not directly constitute a C sink, it can significantly alter the transient apparent soil CO_2 flux, either in magnitude or in temperature dependency. Thus, recognizing the fact that abiotic component in R_(total) exists widely in soils has widespread consequences for the understanding of C cycling. As an important component of ecosystem carbon (C) budgets, soil carbon dioxide (CO_2) flux is determined by a combination of a series of biotic and abiotic processes. Although there is evidence that the abiotic component can be important in total soil CO_2 flux (R_ (total)), its relative importance has never been systematically assessed. In this study, after comparative measurements of CO_2 fluxes on sterilized and natural soils, the R_ (total) was partitioned into biotic flux (R_ (biotic)) and abiotic flux (R_ (abiotic)) across a broad range of land-cover types (including eight sampling sites: cotton field, hops field, halophyte garden, alkaline land, reservoir edge, native saline desert, dune crest and interdune lowland) in Gurbantunggut Desert , Xinjiang, China. The relative contribution of R_ (abiotic) to R_ (total), as well as the temperature dependency and predominant factors for R_ (total), R_ (biotic) and R_ (abiotic) R_ (abiotic) always contributed t Specifically, the ratio of R_ (abiotic) to R_ (total) was very low in cotton field and hops field and very high in alkaline land and dune crest. Statistically, the ratio of R_ (abiotic) to R_ (total) logarithmically increased with decreasing R_ (biotic), suggesting that R_ (abiotic) strongly affected R_ (total) when R_ (biotic) was low. pattern confirms that soil CO_2 flux is predominated by biotic processes in most soils, but abiotic processes can also be dominant when biotic processes are weak. On a diurnal basis, R_ (abiotic) can not result in net gain or net loss of CO_2, but its effect on transient CO_2 flux was significant. Temperature dependency of R_ (total) varied among the eight sampling sites and was determined by the predominant processes (abiotic or biotic) of CO_2 flux. (abiotic) was regulated by the change i(ie, CO_2 went into soil) while rising temperature (ΔT> 0) resulted in positive R_ (abiotic) (ie, CO_2 Without recognition of R_ (abiotic), R_ (biotic) would be overestimated for the daytime and underestimated for the nighttime. Although R_b (abiotic) may not change the sum or the net value of daily soil CO_2 exchange and may not directly constitutes a C sink, it can significantly alter the transient apparent soil CO_2 flux, either in magnitude or in temperature dependency. Thus, recognizing the fact that abiotic component in R_ (total) exists widely in soils has extensive consequences for the understanding of C cycling.